var myWin = null;
function openwin(url, name) {

if ((myWin == null) || (myWin.closed)) {

    myWin = window.open(url, name, "toolbar=no, location=no, directories=no, status=no, menubar=no, resizable=yes, scrollbars=yes, width=500, height=400");
  }
  else {
        myWin.location.href = url;
  }

}